1. Field of the Invention
The invention relates to hoists for lifting objects such as automobiles and trucks and, more particularly, to a hoist employing I-beam construction to a substantial extent, individual drive means for lifting the corners of a lifting frame, and other novel features.
2. Description of the Prior Art
Above-ground hoists adapted for lifting vehicles such as automobiles, trucks, and so forth have been known for some time. These devices typically take the form of a plurality of vertically oriented posts to which a lifting frame is secured in sliding relationship. The lifting frame is configured such that a vehicle can be driven onto or over the lifting frame and, upon raising the lifting frame, the vehicle will be lifted. Various types of driving mechanisms have been provided to raise and lower the lifting frame, such arrangements generally being used in the form of vertically extending threaded rods carried by the posts. Each rod carries a nut secured to a corner of the lifting frame such that, upon rotation of the rod, the nut and hence the lifting frame is raised or lowered as desired. Other driving arrangements for the lifting frame include an endless cable or chain reeved about pulleys or sprockets connected to driving gear arrangements located at the corners of the lifting frame. At least one other known driving arrangement employs vertically oriented hydraulic cylinders secured to the lifting frame to raise and lower the lifting frame.
The aforementioned hoists, although functioning more or less effectively to raise and lower a vehicle, still fail to address certain problems. One problem not adequately addressed by prior hoists is that of providing a strong structure, while at the same time keeping the structure relatively inexpensive and easy to assemble. In certain cases portions of the lifting frame are securely yet slidably connected to the posts such that, upon vertical motion of the lifting frame, the posts will be connected to each other rigidly. A problem with this approach is that specially formed interlocking parts are required to properly mate the lifting frame and the posts, and wear of these parts can adversely affect the strength and efficiency of the hoist. It is desirable that the lifting frame be slidably connected to the posts with a minimum of specially formed, carefully sized parts without sacrificing the stability of the hoist.
Another problem not adequately addressed by prior art devices is the technique by which the lifting frame is moved vertically. Generally speaking, the prior art endless cable and hydraulic cylinder arrangements have been unduly expensive and difficult to assemble. Moreover, a failure of an endless chain or cable can result in the entire lifting frame falling or becoming disabled.
Yet another consideration not adequately addressed by prior art hoists relates to the construction of the lifting frame and the techniques by which it can be adjusted to fit different vehicles. Most prior lifting frames engage the frame of the vehicle, rather than the wheels of the vehicle. In other words, the vehicle is driven over the frame and the lifting frame is raised until the body of the vehicle is contacted. Such an arrangement can be a drawback in those instances where portions of the vehicle's engine, transmission, exhaust system, and so forth must be serviced. This is because the lifting frame can obstruct the parts needing repair and, accordingly, the repair work can be made unnecessarily difficult. Although it is known to provide a lifting frame having runways upon which the wheels of a vehicle can be supported, such lifting frames have been difficult to manufacture and adjust. Moreover, runway-type-lifting frames have not included safety systems to prevent the lifting frame from becoming excessively unbalanced.